The invention relates to a test rig and a process for testing motor-vehicle assemblies, in particular independent wheel suspensions of motor vehicles, under operational loading condition.
Chassis components of motor vehicles such as stub axles, wishbones, tie rods, fastening elements, axle hubs, body components or frame components are, in the course of driving operations, subject to complex, multi-axial stresses. The forces acting on the chassis are vertical forces F.sub.Z, lateral forces F.sub.Y, longitudinal forces F.sub.X and braking or driving forces F.sub.XB, the points of force application are shown in FIGS. 1 and 2 with reference to an automobile.
For different loading cases, the forces listed above differ as regards their relevance (correlation) and frequency. Typical loading cases occurring in the course of motoring operation, which must be taken into account in the process of simulation, are:
1. Driving straight ahead on roads with different surface characteristics, where the principal forces coming into play are vertical forces as well as lateral forces and longitudinal forces.
2. Cornering, where the main forces coming into play are vertical forces and lateral forces.
3. Braking and propulsion, where the main forces coming into play are vertical forces, as well as braking or driving forces.
For testing individual chassis components hitherto, use has so far predominantly been made of test rigs designed for uni-axial loading, which do not take into account either the additional deformations due to the compound arrangement or the complex multi-axial stresses due to multi-axial loading and different points of force application.
However, test rigs for multi-axial loading are also known, such as the rig described in the applicant's EP 0 094 570 B1, which describes an arrangement for simulating the operational stresses in vehicles or vehicle assemblies, it being possible simultaneously to induce by means of said arrangement vertical forces, lateral forces, longitudinal forces and braking or driving forces in a motor vehicle or a motor-vehicle assembly so that entire axle structures or entire vehicles can be tested with the aid of said test rig or other known multi-axial test rigs, whereby the various forces such as vertical force F.sub.Z, lateral force F.sub.Y, longitudinal force F.sub.X and braking or driving force F.sub.XB are transmitted to the motor vehicle assembly via servo-hydraulic actuator devices.
Complex control signals are required for controlling said servo-hydraulic actuator devices in order to simulate the various operational loading conditions such as driving straight ahead, cornering, braking and acceleration. In the process of simulation it is also essential to take appropriate account of the frequency of the various loading conditions in order to ensure that the test corresponds to overall loading conditions such as occur in operational usage.
With a multi-axial loading device for inducing vertical forces, lateral forces, longitudinal forces and braking or driving forces, the requisite complex control signals necessary for controlling the servo-hydraulic actuators have, so as to be able to simulate operational loading conditions, to be obtained at the cost of much time and labour by making measurements on an appropriate motor vehicle during driving operation, it also being necessary to adapt said control signals to the given test rig by carrying out iterative procedures and to process them so as to produce a programme for controlled loading.
An adaptive control process is disclosed in ATZ Automobiltechnische Zeitschrift 82 (1980) 9, pages 469 to 473, which can be applied to test rigs of the most varied multi-axial types for testing operational strength with regard to bodies, chassis or entire vehicles in order to simulate measured operational stresses realistically. It is possible to reproduce driving conditions with considerable accuracy by making use of fast digital computers which calculate the design values for the analogue control loops used, while taking into account the vibration characteristics of the system. Also by means of this adaptive control process, the control signals required for controlling the servo-hydraulic actuators of the rig for testing operational strength must in the given case be obtained from measurements carried out, during operation, on the vehicle type under study and must be adapted by iterative procedures to the given rig for testing operational strength in order to produce a control loading programme.
However, such a control loading programme can only be used for motor-vehicle assemblies of that special type of motor vehicle (i.e. with special vehicle characteristics and special vehicle size), which was used to make the above measurements during operation of the vehicle, as well as for those operational uses and axle loads which applied when said measurements during motoring operation were carried out.
For testing motor-vehicle assemblies pertaining to a different type of motor vehicle and/or with different axle loads and/or different operational uses appropriate labour- and time-intensive measurements during vehicle operation as well as iterative procedures must again be carried out in the given case so as to obtain an appropriate control loading programme. The transfer or adaptation of a control loading programme derived with respect to a given type of motor vehicle, specific axle loads and certain operational usage to a different type of motor vehicle, other axle loads and/or other operational usage can only be effected, due to different design and/or different vibration characteristics of the motor-vehicle where this is at all possible given the present state of the art, with considerable restrictions and difficulties and at considerable expense.
EP 0 220 794 B1 describes, with respect to a rig for testing multi-axial operational strength, the way in which the control signals work during operation of the test rig, but it does not explain in detail how these control signals are obtained.
DE 40 14 876 A1 describes a process and a device for determining and/or monitoring the state of a technical component of a motor vehicle in relation to the body, in particular of the tires with respect to tire inflation pressure and/or of the shock absorbers with respect to shock-absorber defects, by measuring vibrations induced in the chassis of the motor vehicle with respect to parts of the wheel suspension. This is not at all a matter of controlling force-generators pertaining to a rig for testing operational strength but of making actual measurements on a motor vehicle during normal vehicle operation, where measured values detected by sensors are processed in a computer by means of an algorithm and compared with stored previous measured values or computer results.
Lastly, DE 30 25 478 A1 describes a loading test rig for vehicle axles comprising control devices which scan and regulate the movements due to the loading in order to obtain a desired loading. This loading test rig is directly associated with the vehicle to be tested. This specification says nothing about the production of a control loading programme but is merely concerned with producing, in the given case, a required loading of a given vehicle by means of regulating processes.